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Approaches To Classification of Climate
Three broad approaches have been adopted for classifying climate:
i). Empirical classification is based on observed data, particularly on temperature and precipitation.
ii). Genetic classification attempts to organize climates according to their causes.
iii). Applied classification is for specific purpose.
Koeppen’s Scheme Of Classification Of Climate
1). Identified a close relationship between the distribution of vegetation and climate.
2). It is based on mean annual and mean monthly temperature and precipitation data.
3). Climate groups according to Koppen:
Group Characteristics
i). A - Tropical || Average temperature of the coldest month is 18° C or higher
ii). B - Dry Climates || Potential evaporation exceeds precipitation
iii). C - Warm Temperate || The average temperature of the coldest month of the (Mid-latitude) climates years is higher than minus 3°C but below 18°C
iv). D - Cold Snow Forest Climates || The average temperature of the coldest month is minus 3° C or below
v). E - Cold Climates || Average temperature for all months is below 10° C
vi). H - High Land || Cold due to elevation.
4). The capital letters: A, C, D and E delineate humid climates and B dry climates.
5). The climatic groups are subdivided into types, designated by small letters, based on seasonality of precipitation and temperature characteristics.
6). The seasons of dryness are indicated by the small letters: f, m, w and s, where f corresponds to no dry season m - monsoon climate, w- winter dry season and s- summer dry season.
7). The small letters a, b, c and d refer to the degree of severity of temperature.
8). The B- Dry Climates are subdivided using the capital letters S for steppe or semi-arid and W for deserts.
9). Climate group types according to Koppen are:
Group || Type || Letter code || Characteristics
i). A- tropical Humid Climate || Tropical wet, Tropical monsoon, Tropical wet and dry || Af, Am, Aw || No dry Season, Monsoonal, short dry season, Winter dry season
ii). B- Dry Climate || Subtropical steppe, Subtropical desert, Mid-latitude steppe, Mid-latitude desert || BSh, BWh, BSk, BWk || Low-latitude semi-arid or dry, Low-latitude arid or dry, Mid-latitude semi-arid or dry, Mid-latitude arid or dry
iii). C-Warm Temperate(mid latitude)climate || Humid subtropical, Mediterranean, Marine west coast || Cfa, Cs, Cfb || No dry season, warm summer, Dry hot summer, No dry season, warm and cool summer
iv). D-Cold snow - Forest Climate || Humid continental, subarctic || Df, Dw || No dry season, severe winter || Winter dry and very severe
v). E-Cold Climates || Tundra, Polar ice cap || ET, EF || No true summer, Perennial ice
vi). H-Highland || Highland || H || Highland with snow cover
Group A : Tropical Humid Climates
i). Tropical humid climates exist between Tropic of Cancer and Tropic of Capricorn.
ii). The sun being overhead throughout the year and the presence of Inter Tropical Convergence Zone (ITCZ) make the climate hot and humid.
iii). Annual range of temperature is very low and annual rainfall is high.
iv). The tropical group is divided into three types, namely:
(A) Af- Tropical wet climate;
(B) Am - Tropical monsoon climate;
(C) Aw- Tropical wet and dry climate.
Tropical Wet Climate(Af)
(a). Tropical wet climate is found near the equator.
(b). The major areas are the Amazon Basin in South America, western equatorial Africa and the islands of East Indies.
(c). Significant amount of rainfall occurs in every month of the year as thunder showers in the afternoon.
(d). The temperature is uniformly high and the annual range of temperature is negligible.
(e). The maximum temperature on any day is around 30°C while the minimum temperature is around 20°C.
(f). Tropical evergreen forests with dense canopy cover and large biodiversity are found in this climate.
Tropical Monsoon Climate (Am)
It is found over the Indian sub-continent, North Eastern part of South America and Northern Australia. Heavy rainfall occurs mostly in summer and winter is dry.
Tropical Wet and Dry Climate (Aw)
(a). Occurs north and south of Af type climate regions.
(b). It borders with dry climate on the western part of the continent and Cf or Cw on the eastern part.
(c). Extensive Aw climate is found to the north and south of the Amazon forest in Brazil and adjoining parts of Bolivia and Paraguay in South America, Sudan and south of Central Africa.
(d). The annual rainfall in this climate is considerably less than that in Af and Am climate types and is variable also.
(e). The wet season is shorter and the dry season is longer with the drought being more severe.
(f). Temperature is high throughout the year and diurnal ranges of temperature are the greatest in the dry season.
(e). Deciduous forest and tree-shredded grasslands occur in this climate.
Dry Climate
i). Characterized by very low rainfall that is not adequate for the growth of plants.
ii). These climates cover a very large area of the planet extending over large latitudes from 15° - 60° north and south of the equator.
iii). At low latitudes, from 15° - 30°, they occur in the area of subtropical high where subsidence and inversion of temperature do not produce rainfall.
iv). On the western margin of the continents, adjoining the cold current, particularly over the west coast of South America, they extend more equator wards and occur on the coast land.
v). In middle latitudes, from 35° - 60° north and south of equator, they are confined to the interior of continents where maritime-humid winds do not reach and to areas often surrounded by mountains.
vi). Dry climates are divided into steppe or semi-arid climate (BS) and desert climate (BW).
vii). They are further subdivided as subtropical steppe (BSh) and subtropical desert (BWh) at latitudes from 15° - 35° and mid-latitude steppe (BSk) and mid-latitude desert (BWk) at latitudes between 35°- 60°.
Subtropical Steppe (BSh) and Subtropical Desert (BWh)
a). Both have common temperature and precipitation characteristics.
b). Subtropical steppe region receives slightly more rainfall than the subtropical desert which is sufficient enough for the growth of sparse grasslands.
(c). The rainfall in both the climates is highly variable. Rain occurs in short intense thundershowers in deserts and is futile in building soil moisture.
(d). The inconsistency in the rainfall distresses the life in the steppe much more than in the desert, more frequently causing famine.
(e). Fog is common in coastal deserts neighbouring cold currents.
(f). The maximum temperature in this region in summer is very high, and the annual and diurnal ranges of temperature are also high.
(g). The highest temperature of 58°C was recorded in 1922 at Al Aziziyah in Libya. This region is positioned in the transition zone between dry climates and humid.
Warm Temperatures
Extend from 30° - 50° of latitude mainly on the eastern and western margins of continents. These climates generally have warm summers with mild winters.
i). Humid subtropical, i.e. dry in winter and hot in summer (Cwa);
ii). Mediterranean (Cs);
iii). Humid subtropical, i.e. no dry season and mild winter (Cfa);
iv). Marine west coast climate (Cfb)
Humid Subtropical Climate (Cwa)
Occurs pole ward of Tropic of Cancer and Capricorn, mainly in North Indian plains and South China interior plains. The climate is similar to Aw climate except that the temperature in winter is warm.
Mediterranean sea (Cs)
(a). Occurs around Mediterranean sea, along the west coast of continents in subtropical latitudes between 30° - 40° latitudes. Central California, Central Chile, along the coast in south eastern and south western Australia.
(b). These areas come under the influence of subtropical high in summer and westerly wind in winter. Hence, the climate is characterized by hot, dry summer and mild, rainy winter.
(c). Monthly average temperature in summer is around 25° C and in winter below 10°C.
(d). The annual precipitation ranges between 35 - 90 cm.
Humid Subtropical Climate (Cfa)
(a). Climate lies on the eastern parts of the continent in subtropical latitudes.
(b). In this region the air masses are generally unstable and cause rainfall throughout the year. They occur in eastern United States of America, southern and eastern China, southern Japan, north- eastern Argentina, coastal south Africa and eastern coast of Australia.
(c). The annual averages of precipitation vary from 75-150 cm.
(d). Thunderstorms in summer and frontal precipitation in winter are common.
(e). Mean monthly temperature in summer is around 27°C, and in winter it varies from 5°-12° C.
Marine West Coast Climate (Cfb)
(a). Marine west coast climate is located poleward from the Mediterranean climate on the west coast of the continents.
(b). The main areas are: Northwestern Europe, West Coast of North America, North of California, Southern Chile, South- Eastern Australia and New Zealand.
(c). Due to marine influence, the temperature is moderate and in winter, it is warmer than for its latitude.
(d). The mean temperature in summer months ranges from 15°-20°C and in winter 4°-10°C.
(e). The annual and daily ranges of temperature are small.
(f). Precipitation occurs throughout the year. Precipitation varies greatly from 50-250cm.
Cold Snow Forest(D)
Cold snow forest climates occur in the large continental area in the northern hemisphere between 40°-70° north latitudes in Europe, Asia and North America. Cold snow forest climates are divided into two types:
i). Df- cold climate with humid winter;
ii). Dw- cold climate with dry winter
Cold Climate with Humid Winters (Df)
(a). Cold climate with humid winter occurs poleward of marine west coast climate and mid latitude steppe. The winters are cold and snowy.
(b). The frost free season is short, and the annual ranges of temperature are large.
(c). The weather changes are abrupt and short, and Poleward - the winters are more severe.
Cold Climate with Dry Winters (Dw)
(a). Cold climate with dry winter occurs mainly over Northeastern Asia.
(b). The development of pronounced winter anti cyclone and its weakening in summer sets in monsoon like reversal of wind in this region.
(c). Poleward summer temperatures are lower and winter temperatures are extremely low with many locations experiencing below freezing point temperatures for up to seven months in a year.
(d). Precipitation occurs in summer and the annual precipitation is low from 12-15 cm.
Polar Climates (E)
Polar climates exist poleward beyond 70° latitude. Polar climates consist of two types:
i). Tundra (ET);
ii). Ice Cap (EF).
Tundra Climate (ET)
(a). The tundra climate (ET) is so called aer the types of vegetation, like low growing mosses, lichen and flowering plants.
(b). This is the region of permafrost where the subsoil is permanently frozen. The short growing season and water logging support only low growing plants.
(c). During summer, the tundra regions have very long duration of daylight.
Ice Cap Climate (EF)
(a). The ice cap climate (EF) occurs over interior Greenland and Antarctica.
(b). Even in summer, the temperature is below freezing point.
(c). This area receives very little precipitation. The snow and ice get accumulated and the mounting pressure causes the deformation of the ice sheets and they break.
(d). They move as icebergs that float in the Arctic and Antarctic waters. Plateau Station , Antarctica ,79°S, portray this climate.
Highland Climates (H)
i). It is governed by topography.
ii). In high mountains, large changes in mean temperature occur over short distances.
iii). Precipitation types and intensity also vary spatially across highlands.
iv). There is vertical zonation of layering of climatic types with elevation in the mountain environment.
Climate Change
i). The type of climate we experience now might be prevailing over the last 10,000 years with minor and occasionally wide fluctuations.
ii). India witnessed alternate wet and dry periods.
iii). Archaeological findings show that the Rajasthan desert experienced wet and cool climate around 8,000 B.C. The period 3,000-1,700 B.C. had higher rainfall. From about 2,000-1,700 B.C., this region was the centre of the Harappan civilization. Dry conditions since then.
iv). During the Pleistocene epoch, glacial and interglacial periods occurred, the last major peak glacial period was 18,000 years ago.
v). The present interglacial period started 10,000 years ago.
Climate In Recent Past
Variability in climate occurs all the time. The nineties decade of the last century witnessed extreme weather events. Effects of climate change are crop yield or crop failures, floods and migration of people.
i). The worst devastating drought in the Sahel region, south of the Sahara desert, from 1967-1977 is one such variability.
ii). A number of times Europe witnessed warm, wet, cold and dry periods, especially during the tenth and eleventh centuries.
iii). Variability in climate occurs all the time. The 1990s recorded the warmest temperature of the century and some of the worst floods around the world.
iv). During the 1930s, severe drought occurred in southwestern Great Plains of the United States, described as the dust bowl.
Causes Of Climate Change
The causes for climate change are many, they can be grouped into astronomical and terrestrial causes.
(a). The astronomical causes are the changes in solar output associated with sunspot activities. Sunspots are dark and cooler patches on the sun which increase and decrease in a cyclical manner.
(b). According to some meteorologists, when the number of sunspots in crease, cooler and wetter weather and greater storminess occur.
(c). Another astronomical theory is Milankovitch oscillations, which infer cycles in the variations in the earth’s orbital characteristics around the sun, the wobbling of the earth and the changes in the earth’s axial tilt. Alter insolation from the sun.
(d). Volcanic eruptions throw up lots of aerosols into the atmosphere and reduce sun radiations reaching earth.
(e). Anthropogenic effect: Higher concentration of CO2 leading to global warming.
Global Warming
i). Due to the presence of greenhouse gases, the atmosphere is behaving like a greenhouse.
ii). The atmosphere also transmits the incoming solar radiation but absorbs the vast majority of long wave radiation emitted upwards by the earth’s surface. The gases that absorb long wave radiation are called greenhouse gases.
iii). Greenhouse: The processes that warm the atmosphere are often collectively referred to as the greenhouse effect. The term greenhouse is derived from the analogy to a greenhouse used in cold areas for preserving heat. A greenhouse is made up of glass. The glass which is transparent to incoming shortwave solar radiation is opaque to outgoing long wave radiation. The glass, therefore, allows in more radiation and prevents the long wave radiation going outside the glass house, causing the temperature inside the glasshouse structure warmer than outside.
Greenhouse Gases
i). The primary GHGs are Carbon dioxide, Chlorofluorocarbons, Methane, Nitrous oxide, Carbon monoxide which easily react with the GHGs and affect their concentration in the atmosphere.
ii). Due to greenhouse gases, earth behaves as a greenhouse, due to which transmission of incoming shortwave solar radiation but absorb longwave radiations going out (allow temperature inside to rise).
iii). The CFC are highly effective. Ozone which absorbs UV radiation in the stratosphere is very effective in absorbing terrestrial radiation when it is present in the lower troposphere. The CFCs which drift into the stratosphere destroy the ozone. Large depletion of ozone occurs over Antarctica. The depletion of ozone concentration in the stratosphere is called the ozone hole. This allows the ultraviolet rays to pass through the troposphere.
iv). More time GHG molecule remain in the atmosphere, the longer it will take to recover from changes that are brought about by the latter.
v). Forests are the largest carbon sink, photosynthesis, 20-50 years taken to adjust to the changes in source to sink. Rises about 0.5% annually. Concentration doubles over pre-industrial levels. Fossil fuels, combustion lead to CO2.
vi). Kyoto protocol proclaimed in 1997 and ratified in 2005 by 141 nations bounds 35 industrialized nations to reduce emissions by 2012 to 5% less than 1900 levels.
vii). Melting of glaciers, ice caps, rise of sea levels, submergence of islands.
viii). Temperature data is available for Europe with a reference period of 1961-1990 with annual average sea surface temperature of 14 degree Celsius.
ix). Maximum warming during 1901-44 and 1977-99. Globally average temperature at the end of 20th century was 0.6 degree Celsius higher than the 19th century.
x). Seven warmest years in 1856-2000 were during the last decade - with 1998 was the warmest year.
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